RF front-end with integrated T/R switch

ABSTRACT

Disclosed is a transmit/receive circuit arrangement wherein a transceiver circuit including a transmit/receive switch is fabricated on an integrated circuit chip. A matching network is wholly disposed off-chip relative to the integrated circuit chip. In embodiments, at least a portion of the matching network is formed off-chip and a portion of the matching network is formed on-chip.

CROSS REFERENCE TO RELATED APPLICATIONS

The present disclosure claims priority to U.S. Provisional App. No.61/347,112 for filed May 21, 2010, and is incorporated herein byreference in its entirety for all purposes.

BACKGROUND

The present invention relates generally to wireless communicationcircuits, and in particular to transmit and receive switches.

Unless otherwise indicated herein, the approaches described in thissection are not prior art to the claims in this application and are notadmitted to be prior art by inclusion in this section.

One of the more important components in present-day wirelesscommunication equipment is the RF (radio frequency) switch. The purposeof an RF switch is to connect/disconnect an antenna between thetransmitter circuitry and the receiver circuitry. Accordingly, suchswitches are commonly referred to as T/R switches (transmit/receive).T/R designs typically include impedance matching circuitry to direct thehigh power transmit signal to the antenna while at the same timepreventing that signal from entering the sensitive front end of thelocal receiver (transmit mode), and also allowing a low-loss connectionbetween the antenna and the receiver (receive mode).

For wireless applications (e.g., mobile devices) it is desirable toreduce the size of the RF board and to lower the cost. These two goalscan be achieved by fully integrate the T/R switch on-chip; in otherwords using integrated circuit techniques to form the T/R switch on anintegrated circuit (IC) chip. FIG. 6 shows a schematic illustration of aconventional fully integrated on-chip arrangement of a T/R switchcircuit based on CMOS (complementary metal-oxide semiconductor)technology.

The IC chip in FIG. 6 includes a power amplifier which can output atransmit signal to be broadcast by an antenna. A low-noise amplifier canaccept a receive signal that is sensed by the antenna to be amplifiedfor further processing. The power amplifier and low-noise amplifier canbe components which constitutes a transceiver circuit. The circuitarrangement that is between the power amplifier and the low-noiseamplifier can be collectively referred to as the T/R switch. The T/Rswitch includes switch elements (e.g., transistors M_(T), M_(RS), andM_(RP)) and impedance matching components (e.g., inductors such asinductor L_(RS), and capacitors C_(C), C_(RS), and C_(S)). The IC chipincludes a single tx/rx pin to output the transmit signal fortransmission by an antenna and to input a receive signal sensed by theantenna. The switch elements (M_(T), M_(RS), and M_(RP)) control whetherthe transmit signal is output on the tx/rx pin or the signal sensed bythe antenna is input via the tx/rx pin. The impedance matchingcomponents provide impedance matching between the power amplifier andthe antenna, and between the low-noise amplifier and the antenna.

The IC chip is typically assembled on a printed circuit board (PCB), andconnected to an “off-chip” component. For example, a balun(balance-unbalance) filter is a typical off-chip component used with theantenna and is assembled on the PCB along with the IC chip. The singletx/rx pin of the IC chip can be connected to the balun filter via atrace formed on the PCB between the tx/rx pin and a pin on the balunfilter. Alternatively, the tx/rx pin and balun pin can be connected torespective pads on the PCB, and a bonding wire can be soldered to thepads to make the connection.

The quality factors of on-chip matching components, especiallyinductors, are usually quite poor due to metal resistance and lossyproperties of silicon substrates. Poor quality factors result in limitedtransmit power and receive sensitivity performance. With on-chipmatching components, there is loss of flexibility in fine tuning the RFswitch. Since the inductors and capacitors are fabricated on-chip, it isnot practical to vary their component values in case fine tuning isneeded, for example, to accommodate for impedance variations in theantenna/balun filter assembly. In addition, component values of theon-chip matching elements are subject to process variations and thus mayvary from one lot of chips to another. Also, there is loss offlexibility to accommodate different package designs.

These and other issues are addressed by embodiments of the presentinvention, individually and collectively.

SUMMARY

A circuit configuration in accordance with embodiments of the presentinvention includes an integrated circuit (IC) having first and secondswitching elements. The first switching element may provide a transmitsignal to the antenna. The second switching element may receive areceived signal sensed by the antenna. The IC includes a first pin and asecond pin to respectively transmit and receive signals. An off-chipimpedance matching circuit is separate from the IC, but electricallyconnected to the IC. The impedance matching circuit includes a singleelectrical connection to the antenna.

In and embodiment, the impedance matching circuit comprises one or morecapacitive or inductive components.

In an embodiment, the impedance matching circuit can be affixed to aprinted circuit board PCB) and the IC can affixed to the PCB or toseparate PCB.

In an embodiment, the IC includes an on-chip impedance matching network.

In an embodiment, a method for a circuit includes receiving a transmitsignal on an IC chip and outputting the transmit signal to a first pinof the IC chip. The transmit signal is received by an impedance matchingnetwork that is off-chip with respect to the IC chip. The transmitsignal is then output to an antenna via a terminal of the impedancematching network. The method further includes receiving at the terminalof the impedance matching network a received signal sensed by theantenna and outputting the received signal to a second pin of the ICchip. In an embodiment, the received signal is received by a secondamplifier of the IC chip.

A circuit configuration in accordance with embodiments of the presentinvention includes a printed circuit board having disposed on it anantenna assembly, an impedance matching network, and a transceiverintegrated circuit. The impedance matching network includes a singleconnection to the antenna assembly. The transceiver integrated circuitincludes a first amplifier configured to output a transmit signal on afirst pin, and a second amplifier configured to receive a receivedsignal on a second pin. The impedance matching network providesimpedance matching between the first pin and second pin of thetransceiver integrated circuit and the single terminal connected to theantenna assembly.

In an embodiment, the transceiver integrated circuit does not includeany impedance matching network circuitry.

In an embodiment, the transceiver integrated circuit includes on-chipimpedance matching network circuitry.

The following detailed description and accompanying drawings provide abetter understanding of the nature and advantages of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a high level block diagram of the present invention.

FIG. 1B shows an embodiment of the present invention.

FIG. 2 shows alternate circuit configurations in accordance with thepresent invention.

FIG. 3 shows an embodiment of the board matching network.

FIG. 3A shows a particular implementation of the board matching network.

FIG. 4 shows a particular implementation of the board matching networkand the on-chip matching network.

FIG. 5 shows a wireless system incorporating the circuit configurationof the present invention.

FIG. 6 shows a conventional arrangement of T/R switch circuitry.

DETAILED DESCRIPTION

Described herein are illustrative embodiments of a T/R switch circuitarrangement for an RF front-end.

In the following description, for purposes of explanation, numerousexamples and specific details are set forth in order to provide athorough understanding of the present invention. It will be evident,however, to one skilled in the art that the present invention as definedby the claims may include some or all of the features in these examplesalone or in combination with other features described below, and mayfurther include modifications and equivalents of the features andconcepts described herein.

FIG. 1A is a high level block diagram of a transmit/receive (T/R)circuit in accordance with the present invention. A transceiver circuit2 may include a transmit circuit for producing a signal suitable fortransmission by an antenna (in the antenna assembly 6) and receivercircuit for receiving a received signal sensed by the antenna. Thetransceiver circuit 2 may include a transmit/receive switch to switchbetween outputting a transmit signal or receiving a received signal. Amatching network 4 provides impedance matching between the antennaassembly 6 and the transceiver circuit 2 in order to maximize powertransfer, reduce reflection of signals and so on. The antenna assembly 6may include the antenna itself and may include other supportingcircuitry; for example, a balun filter.

Referring to FIG. 1B, a T/R (transmit/receive) circuit arrangement inaccordance with the present invention includes an IC chip 108 comprisingcircuitry for transmitting signals and receiving signals andcorresponding switching circuitry to switch between transmit mode andreceive mode. In an embodiment, the matching network 4 (FIG. 1A) maycomprise board matching network 124 for matching the impedance betweenan antenna 104 and the circuitry in IC chip 108. Further in accordancewith the present invention, the board matching network 124 is “off-chip”with respect to the IC chip 108. In other words, the board matchingnetwork 124 is a component that is not fabricated on the IC chip 108,but rather is a component that is physically separate from the IC chip.In an embodiment, the board matching network 124 is assembled on aprinted circuit board (PCB) 102. The IC chip 108 can be connected to thePCB 102, for example, via bond wires 112, 114. An antenna assemblycomprising the antenna 104 and a balun filter 106 can be assembled onthe PCB 102.

The board matching network 124 may include a terminal 124 a configuredto receive an incoming signal, a terminal 124 b configured to output anoutgoing signal, and terminal 124 c configured to output a signal to betransmitted by the antenna 104 and to receive a signal sensed orotherwise received by the antenna. The bond wires 112, 114 may haveinductive characteristics. Accordingly, in an embodiment, the bond wires112, 114 can be considered part of the board matching network 124.

In embodiments, the IC chip 108 may include a power amplifier 132 and alow-noise amplifier (LNA) 134. The amplifiers 132, 134 can be componentsof a transceiver circuit (not shown). The IC chip 108 may furtherinclude T/R switches 126, 128. For example, the T/R switches 126, 128shown in FIG. 1B are CMOS NPN transistors. A PA T/R switch 126 can beconnected to an output of the power amplifier 132. The PA T/R switch 126can be configured to enable or prevent conduction of the transmit signalalong signal path 116.

An LNA T/R switch 128 can be connected to an input of the amplifier 134.In embodiments, the amplifier 134 can be a low-noise amplifier thatreceives and amplifies a signal sensed by the antenna 104. The LNA T/Rswitch 128 can be configured to enable or prevent conduction, inresponse to a control signal (rx control), of the sensed signalappearing at an output 122 d of an on-chip matching network 122(discussed below) to an input of the amplifier 134.

In a transmit mode of operation, a signal to be transmitted (tx signal)is provided to the power amplifier 132. The output of the poweramplifier 132 constitutes a transmit signal that essentially followssignal path 116 toward the antenna 104, where it is broadcast. In areceive mode of operation, signals sensed (i.e., received) by theantenna 104 essentially follows signal path 118 toward the amplifier134. The amplifier 134 amplifies the sensed signal to produce an outputthat constitutes a received signal (rx signal) which can be provided todownstream circuits (not shown) for further processing.

As mentioned above, in accordance with the present invention, thematching network 4 comprises board matching network 124. In embodiments,the matching network 4 may further comprise the on-chip impedancematching network 122 fabricated on the IC chip 108. The on-chip matchingnetwork 122 may include a terminal 122 a configured to receive viaswitch 126 the output (transmit signal) of the power amplifier 132.Terminals 122 b and 122 c may be connected to respective external pins(not shown) of the IC chip 108. The terminal 122 b is configured tooutput the transmit signal to the external pin. The terminal 122 c isconfigured to receive the signal sensed by the antenna 104. A terminal122 d is configured to provide the signal sensed by the antenna 104 toamplifier 134. The bond wires 112, 114 may have inductivecharacteristics. Accordingly, in an embodiment, the bond wires 112, 114can be considered part of the board matching network 124.

Referring to FIG. 2A, in embodiments, the IC chip 108 can be assembledon the same PCB 102 as the board matching network 122, and connectedtogether by traces 202 formed on the PCB 102. The antenna 104 can beprovided separate from the PCB 102. In FIG. 2B, an embodiment is shownwherein the IC chip 108 can be assembled on a PCB 102 a different fromthe PCB 102. A suitable connector 204 (e.g., flex connector) can be usedto connect the PCB 102 and the PCB 102 a. It will be appreciated thatthe matching network (either on-chip matching network 122 or boardmatching network 124, or both) can be further configured to account ofthe impedance present in the connector 204. A magnified area of FIG. 2Cshows the bond wire 112, 114 connections to the traces 202.

Referring to FIG. 3, in an embodiment, all of the impedance matchingcomponents of the matching network 6 (FIG. 1) can be provided by theboard matching network 124. In other words, all of the matchingcomponents are “off-chip” in that none of the matching components arefabricated on the IC chip 108. In this embodiment, the on-chip matchingnetwork 122 in the IC chip 108 is effectively absent, comprising onlytraces 122 x formed in a metal layer of the IC chip. The board matchingnetwork 124 comprises reactive elements X₁-X₃, and can be any suitablecombination of inductors and/or capacitors.

During receive mode operation, the PA T/R switch 126 and the LNA T/Rswitch 128 are OFF, so that signals sensed by the antenna 104 willessentially follow signal path 118. Accordingly, the impedances thatarise include the input impedance of the low-noise amplifier 134 seen atterminal 124 b and some parasitic impedance seen at element X₂. The X₁and X₃ elements constitute an L-matching network and can be designedwith element values based on the input impedance of the low-noiseamplifier 134 and the parasitic impedance to transform those impedancesto match the impedance of the antenna 104 and balun filter 106 assembly,for example 50Ω.

During transmit mode operation, the PA T/R switch 126 and the LNA T/Rswitch 128 are ON; the LNA T/R switch acts as a shunt to ground, thusbypassing the input to the low-noise amplifier 134. Accordingly, theimpedances that arise during include the low impedance path (e.g.,several ohms) seen at terminal 124 b due to the shunt. The X₁ elementtogether with the X₂ and X₃ elements can be designed to be resonant withthe balun filter 106 at the transmit frequency, thus maximizing thetransmit output power delivered to the antenna 104.

FIG. 3A shows an example of a more specific embodiment. Capacitors C2and C3 and inductor L1 are provided off-chip. For example, capacitors C2and C3, and inductor L1 can be discrete components. Capacitors C2 and C3can be IC components provided in discrete form and are assembledoff-chip. The particular embodiment shown in FIG. 3A offers maximumflexibility in terms of accommodating changes to the matching network 6because it is contained off-chip in board matching network 124. However,the cost of having exclusively off-chip components may constitute anunacceptable cost in manufacture. For example, while low-cost discreteoff-chip capacitors may be available, discrete inductors tend to be moreexpensive.

In an embodiment, the matching network 6 (FIG. 1) may comprise on-chipcomponents, namely some of the components of the matching network may beintegrated on the IC chip 108. Accordingly, the embodiment shown in FIG.4 provides a board matching network 124 comprising capacitors C2, C3 andan on-board matching network 12 comprising inductor L1. The inductor L1fabricated on the IC chip 108; i.e., it is on-chip as compared to thecapacitors C2, C3 which are off-chip. This configuration may be moreacceptable in terms of manufacturing costs. For example, the inductor L1may be on the order of a few nano-Henries which lends itself to thepossibility of integration. The cost of a discrete component vs. thedegradation of performance of an integrated circuit version of thecomponent may weigh in favor of integration.

FIG. 5 illustrates a wireless communication system 502 incorporating anembodiment of the present invention. For example, wireless communicationsystem 502 can be any handheld device such as a mobile communicationdevice (e.g., cellular telephone), a computing device having wirelesscommunication capability (e.g., laptop, notebook computer), a handheldgaming device having wireless communication capability (e.g., iPod Touchmanufactured and sold by Apple Inc.), and so on. The wirelesscommunication system 502 can use any communication standard such as thevarious IEEE 802 formats (e.g., Bluetooth, 802.11n, 802.11g and so on).

As used in the description herein and throughout the claims that follow,“a”, “an”, and “the” includes plural references unless the contextclearly dictates otherwise. Also, as used in the description herein andthroughout the claims that follow, the meaning of “in” includes “in” and“on” unless the context clearly dictates otherwise.

The above description illustrates various embodiments of the presentinvention along with examples of how aspects of the present inventionmay be implemented. The above examples and embodiments should not bedeemed to be the only embodiments, and are presented to illustrate theflexibility and advantages of the present invention as defined by thefollowing claims. Based on the above disclosure and the followingclaims, other arrangements, embodiments, implementations and equivalentswill be evident to those skilled in the art and may be employed withoutdeparting from the spirit and scope of the invention as defined by theclaims.

What is claimed is:
 1. A transceiver circuit comprising: an integrated circuit comprising a first switch configured to transmit a first signal via an antenna, a second switch, a first pin configured to receive the first signal from the first switch, and a second pin configured to receive a second signal; and an impedance matching network separate from and connected to the integrated circuit via the first pin and the second pin, wherein the impedance matching network is connected to the antenna, and wherein the impedance matching network is configured to receive the first signal from the first switch via a first bond wire, wherein the first bond wire is connected between the first pin and the impedance matching network, receive the second signal via the antenna, and forward the second signal to the second switch via a second bond wire, wherein the second bond wire is connected between the second pin and the impedance matching network.
 2. The transceiver circuit of claim 1, wherein the impedance matching network comprises a capacitance and an inductance.
 3. The transceiver circuit of claim 1, wherein: the integrated circuit is affixed to a printed circuit board; and the impedance matching network is affixed to the printed circuit board.
 4. The transceiver circuit of claim 1, wherein: the integrated circuit is affixed to a first printed circuit board; and the impedance matching network is affixed to a second printed circuit board.
 5. The transceiver circuit of claim 1, wherein: the integrated circuit includes a second impedance matching network; and the first pin, the second pin, the first switch, and the second switch are connected to the second impedance matching network.
 6. The transceiver circuit of claim 1, wherein the integrated circuit comprises: a first amplifier comprising an output connected to the first switch, wherein the first amplifier is configured to output the first signal to the first switch; and a second amplifier comprising an input connected to the second switch, wherein the second amplifier is configured to receive the second signal from the second switch.
 7. The transceiver circuit of claim 1, further comprising a filter connected between the antenna and the impedance matching network.
 8. A wireless communication system comprising the transceiver circuit of claim
 1. 9. A method comprising: receiving a first signal from an integrated circuit at an impedance matching network, wherein the impedance matching network is separate from and connected to the integrated circuit via a first bond wire, and wherein the first bond wire is connected between (i) a first pin on the integrated circuit and (ii) the impedance matching network; transmitting the first signal from the impedance matching network via an antenna; receiving a second signal at the impedance matching network via the antenna; and transmitting the second signal from the impedance matching network to the integrated circuit via a second bond wire, wherein the second bond wire is connected between (i) a second pin of the integrated circuit and (ii) the impedance matching network.
 10. The method of claim 9, further comprising: amplifying the first signal via a first amplifier prior to transmitting the first signal via the antenna, wherein the integrated circuit comprises the first amplifier; and amplifying the second signal via a second amplifier subsequent to receiving the second signal via the antenna, wherein the integrated circuit comprises the second amplifier.
 11. The method of claim 9, wherein the impedance matching network comprises a capacitance and an inductance.
 12. The method of claim 9, wherein the integrated circuit and the impedance matching network are affixed to a printed circuit board.
 13. The method of claim 9, wherein: the integrated circuit is affixed to a first printed circuit board; and the impedance matching network is affixed to a second printed circuit board.
 14. The method of claim 9, further comprising filtering the first signal via a balun filter prior to transmitting the first signal via the antenna.
 15. A transceiver circuit comprising: a printed circuit board; an antenna assembly comprising a filter, wherein the filter is mounted on the printed circuit board; an impedance matching network mounted on the printed circuit board, wherein the impedance matching network is connected to the antenna assembly; and an integrated circuit comprising a first pin, a second pin, a first amplifier configured to (i) amplify a first signal, and (ii) transmit the first signal to the impedance matching network via the first pin, and a second amplifier configured to receive (i) a second signal from the impedance matching network via the second pin, and (ii) amplify the second signal, wherein the impedance matching network is configured to provide impedance matching between (i) the first pin and the second pin, and (ii) the filter.
 16. The transceiver circuit of claim 15, wherein the integrated circuit is absent an impedance matching network.
 17. The transceiver circuit of claim 15, wherein the integrated circuit includes a second impedance matching network.
 18. The transceiver circuit of claim 1, wherein the impedance matching network comprises: an inductance connected between the antenna and the second bond wire; a first capacitance connected between (i) the antenna and the inductance and (ii) the first bond wire; and a second capacitance connected between (i) the antenna, the inductance, and the first capacitance and (ii) a ground reference.
 19. The transceiver circuit of claim 18, wherein the integrated circuit comprises: a first amplifier configured to amplify the first signal; the first switch configured to forward the first signal from the first amplifier to the first bond wire; the second switch connected between the second bond wire and a ground reference; and a second amplifier connected to the second bond wire and the second switch, wherein the second amplifier is configured to amplify the second signal.
 20. The transceiver circuit of claim 1, wherein the impedance matching network comprises: a first capacitance connected between the antenna and the first bond wire; and a second capacitance connected between (i) the antenna, the second bond wire, and the first capacitance and (ii) a ground reference.
 21. The transceiver circuit of claim 20, wherein the integrated circuit comprises: a first amplifier configured to amplify the first signal; the first switch configured to forward the first signal from the first amplifier to the first bond wire; an inductance connected to the second bond wire; the second switch connected between the inductance and a ground reference; and a second amplifier connected to the inductance and the second switch, wherein the second amplifier is configured to amplify the second signal.
 22. The transceiver circuit of claim 1, further comprising a printed circuit board separate from the integrated circuit, wherein: the impedance matching circuit is mounted on the printed circuit board; the printed circuit board comprises a third pin connected to the impedance matching circuit, and a fourth pin connected to the impedance matching circuit; the first bond wire (i) extends between the integrated circuit and the printed circuit board, and (ii) connects the first pin to the third pin; and the second bond wire (i) extends between the integrated circuit and the printed circuit board, and (ii) connects the second pin to the fourth pin.
 23. The transceiver circuit of claim 15, wherein the integrated circuit is separate from the printed circuit board. 